Automatic evacuation system for electron tubes



July 14, 1959 c, MARSDEN, JR 2,894,795

AUTOMATIC EVACUATION SYSTEM FOR ELECTRON TUBES Filed May 25, 1955 I 2 Sheets-Sheeti it H I]. E E m a, o\ 3 0. up V e m E N n O INVENTOR CHARLES R MARSDEMJR.

TTORNEYS July 14, 1959 c. P. MARSDEN,- JR v 2,894,795

AUTOMATIC EVACUATION SYSTEM FOR ELECTRON TUBES Filed May 23, 1955 2 She ets-Sheet 2 INVENTOR CHARL E5 R MA RSDEN, JR.

ATTORNEYS 2,894,795 Patented July 14, 1959 AUTOMATIC EVACUATION SYSTEM FOR ELECTRON TUBES Charles P. Marsden, Jr., Washington, D.C., assignor to the United States of America as represented by the Secretary of the Navy Application May 23, 1955, Serial No. 510,593

9 Claims. (Cl. 316-30) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.

The present invention relates to an automatic evacuation system for electron tubes and more particularly to an automatic evacuation system for electron tubes wherein a high vacuum is obtained without the use of gates, locks or other closure members for the system.

In the prior art, machines for evacuating electron tubes in the course of their production are known, but these machines have several undesirable characteristics, such as a production rate of 250500 per hour, complex mechanical mechanisms and rotating vacuum-tight flanges.

The present invention contemplates a relatively simple tubular system having no gates or ports at its ends, and having vacuum pump connecting lines along its length, whereby article carriers may be inserted into one end and withdrawn from the other in a continuous stream. The present system therefore, permits a high rate of production, such as 500-1000 per hour, by providing a simplicity of mechanical design. There are no diflicultto-obtain vacuum seals at rotating flanges, no bell jars and no gates or locks in the present invention.

An object of the present invention, therefore, is to overcome the above noted and other deficiencies by providing a simple, high capacity automatic evacuation systern.

Another object is to provide an evacuation system having an absence of parts, gates and mechanically-moving vacuum seals.

Still another object is to provide a system having a high rate of flow of the evacuated gases as all long, small cross-sectional area, interconnecting tubes are eliminated.

A further object is to provide an evacuation and heating system for use in the production of electron tubes.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein:

Fig. 1 is a schematic view of a preferred embodiment of the invention,

Fig. 2 is an end view of the invention.

Fig. 3 is a perspective view, partly cut away, of the heating section of the system,

Fig. 4 is a plan view of a jig which may be used with the invention, and

Fig. 5 is a cross section taken on line 5-5 of Fig. 4.

Referring now to the drawing, wherein like reference characters designate like parts throughout the several views, there is shown in Fig. 1 an automatic evacuation system comprising a long tube 10 having ends 12 and 14 which are open to atmospheric pressure, end 12 being the inlet end and end 14 being the outlet end. Along the tube 10,.at spaced intervals, are a plurality of connecting tubes 16, 18, 20, 22, 24, 26, 28, 30 and 32, each of which is connected to a vacuum pump, not shown. The connecting tubes 16 to 32 are of large diameter, each being of approximately the same diameter as the tube to which it is connected (10 or 38). The connecting tubes are made very short, preferably approximately two feet in length. In the center section of the tube 10 there is a heating station 34 comprising a tube 10a encased within insulation 36 and an outer tube 38. Tube 10a is connected to leads 40 and 42 from transformer 44.

Electron tubes, such as are shown in my and Frank H. Brewers co-pending application Serial No. 377,748, filed August 31, 1953, and entitled Ceramic Wafer Electronic Tube, are assembled and placed into jigs 46 for transportation through the system. Jig 46, as shown in Fig. 2, has a close fit with tube 10, it being apparent that both the jig 46 and tube 10 are square in cross section, this being the preferred shape. The space between the wall of tube 10 and the wall of the jig 46 is not more than about on three sides.

Referring now to Fig. 3, there is shown the portion of tube 10 adjacent to heating station 34. A single jig 46 is shown, although it Will be understood that in practice other jigs will be contiguous with the one shown. Tube 10 extends through end plate 48 of outer tube 38, and is hermetically sealed thereto, as by welding. Interiorly of outer tube 38 is the insulation 36, which is preferably magnesia fire brick, and which supports heater tube 1011, Which is preferably of Nichrome although other suitable materials such as molybdenum, tungsten, or stainless steel may be used. Transformer lead 40 extends through and is insulated from outer tube 38 and is connected to tube 10a. The top of tube 10a is open and a heat baffle 50 lies over the opening, with connecting tube 24 thereabove. An interdigitated joint 52 connects the tubes 10 and 10a, to permit thermal expansion of tube 10a and smooth passage of the jigs 46. By so arranging baflle 50, and the upward opening of tube 10a, large cross-sectional spaces are available for removal of air and gases removed from the tube material and jigs.

Although jigs 46 may take a number of forms, the preferred form is as shown herein, particular attention being invited to Figs. 4 and 5. Jig 46 has a hole 54 therein to receive an electron tube, a tapered nose portion 56 to permit its passage across joints in tube 10, and

. a flat front 58 and flat back 60 to permit pushing of one jig by another. Jig 46 is preferably made from graphite, a ceramic, or other heat resistant material.

In operation, air and other gases are pumped from the tube 10 through the connecting tubes 16 to 32, and a substantial vacuum is obtained even though the ends 12 and 14 or tube 10 are open, i.e., without gates, valves, etc. The ends 12 and 14 are closed somewhat by the boats 46. The space between the tube walls and boat walls being only about the total area is approximately .14 sq. in. The narrowness of the space limits the speed of the air leaking in, due to the action of the pumps, to its sonic velocity, so that the total leakage at either end is approximately 42 cu. ft. per minute. The degree of vacuum at connecting tube 16 will be approximately 50 mm. of mercury; at tube 18 20 mm.; at tube 20, 10* mm.; at tube 22, 10 mm.; at tube 26, lO- mm.; at tube 28, IO- mm.; at tube 30, 20 mm.; and at tube 32, 50 mm. These station values are typical, and some may be changed or eliminated. Because of the large size of connectlng tubes 16-32 and their short length, the necessary high velocity air flow will be obtained.

In the heater section, the action of the transformer 44 and Nichrome tube 10a are well understood; how ever, in the present invention, the temperature is relatively high, being in the range 1000 C. to 1200 C.

J1gs 46 will be caused to proceed through the tube by any suitable arrangement, such as pushing from the rear, gravity feed, chain drive, etc. A continuous stream of jigs will pass through the system, without the necessity of stopping at gates or like partitions. The electron tubes, or other ar "cl-es carried thereby, will be first evacuated, then heated sealed and finally restored to atmosph 'ic pressure. in the case of electron tubes, the heating causes linown action to take place. such as the decomposition of the cathode, the egassing of the parts. and the vacuum sealing of the tube itself by the melting of solder or equivalent material.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. For instance, it would be possible to make gas-filled tubes (thyratrons, voltage regulators) by arranging that section 38 be lengthened and port 24 be used to admit the gas (argon) for such tubes. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An evacuation system comprising an elongated tube having a uniform square cross-section throughout its length, said tube being unobstructed and having open ends, a plurality of elongated article carrying jigs therein being of uniform square cross-section, the cross-sectional area of each of said jigs being slightly less than the cross-sectional area of the opening of said tube whereby air may enter said tube between said jigs and said tube, and a plurality of vacuum pumps connected to said tube at spaced points therealong the length of said tube serviced by said pumps being sulficient to span a series of said jigs, said pumps producing stations of progressively increasing vacuum proceeding from the vicinity of the ends of said tube toward the intermediate portion thereof, whereby to produce a high vacuum interiorly of said tube the highest vacuum being produced at said intermediate portion the pressure therein being less than 1 mm. of mercury.

2. An evacuation and heating system comprising an inlet tube having an open inlet end and a plurality of vacuum pumps connected thereto at spaced points therealong, the opposite end of said inlet tube lying in a heating chamber comprising an outer tube of relatively large diameter, end plates thereon and insulation therein, a heater tube supported by said insulation in said heating chamber, said inlet tube extending through one said end plate, said heater tube having an interdigitated joint with said inlet tube, means to heat said heater tube, an opening in the upper side of said heater tube and a baffle plate thereabove, a vacuum pump connected to said heating chamber, an outlet tube extending through said other end plate, said outlet tube having an interdigitated joint with said heater tube, vacuum pumps connected to said outlet tube at spaced points therealong, said outlet tube having an open outer end, said tubes being of the same size and cross-section, and a. plurality of article carrying jigs in said tubes of the same cross-section and of approximately the same size as said tubes.

3. In an evacuation system, means forming an elongated passage of uniform cross-section open at both ends, elongated means for carrying articles through said passage, a substantial length of said carrying means having a uniform cross-section and said uniform crosssection having a small clearance in said first mentioned means whereby gas may enter said passage between the inner surface of said passage and said carrying means, the area of said small clearance being such that the en tering gas cannot exceed its sonic velocity, separate gas exhausting means connected to said first mentioned means at spaced intervals therealong the length of said first mentioned means serviced by said exhausting means being sufficient to span a series of said carrying means,

said exhausting means producing stations of progressively increasing vacuum proceeding from the vicinity of the ends of said first mentioned means toward the intermediate portion thereof, said intermediate portion having a pressure therein of less than 1 mm. of mercury, and means to heat said first mentioned means at said intermediate portion thereof to a temperature in excess of l000 C.

4. An evacuation system comprising an elongated tube of. uniform cross-section, exhausting means connected to said tube at spaced intervals therealong, and means to restrict the passage of gas into and within said tube whereby said exhausting means produce stations of progressively increasing vacuum proceeding from the vicinity of the ends of siad tube toward the intermediate portion thereof, said intermediate portion having a pressure therein of less than 1 mm. of mercury, said restricting means comprising a plurality of elongated article carrying jigs the length of said tube serviced by said exhausting means being sufficient to span a series of said jigs, a substantial length of each of said jigs having a uniform transverse cross-sectional area slightly smaller than and of substantially the same shape as said tube, whereby gas may enter said tube between said jigs and said tube the area of clearance between each of said jigs and said tube being such that said entering gas cannot exceed its sonic velocity and may thus be exhausted from said tube by said exhausting means.

5. An evacuation system comprising an elongated tube of uniform cross-section open at both ends, exhausting means connected to said tube at spaced intervals therealong by short, wide connecting passages, and means to restrict the passage of gas into and within said tube whereby said exhausting means produce stations of pro gressively increasing vacuum proceeding from the vicinity of the ends of said tube toward the intermediate portion thereof, said intermediate portion having a pressure therein of less than 1 mm. of mercur, said restricting means comprisiru a plurality of elongated article carrying jigs the length of said tube serviced by said exhausting means being sufficient to span a series of said jigs, a substantial length of each of said jigs having a uniform transverse cross-sectional area slightly smaller than and of substantially the same shape as said tube and means to heat said intermediate portion of said tube and such of said jigs as may be located therein, whereby gas may enter said tube between said jigs and said tube the area of clearance between each of said jigs and said tube being such that said entering gas cannot exceed its sonic velocity and may then be exhausted from said tube by said exhausting means.

6. An evacuation system comprising an elongated tube of uniform crosssection open at both ends, exhausting means connected to said tube at spaced intervals therealong, means to restrict the passage of gas into and within said tube whereby said exhausting means produce stations of progresesively increasing vacuum proceeding from the vicinity of the ends of said tube toward the intermediate portion thereof, said intermediate portion having a pressure therein of less than l0 mm. of mercury said restricting means comprising a plurality of elongated article carrying jigs the length of said tube serviced by said exhausting means being suiticient to span a series of said jigs, a substantial length of each of said jigs having a uniform transverse cross-sectional area slightly smaller than and of substantially the same shape as said tube, and means to heat said intermediate portion of said tube and such of said jigs as may be located therein to a temperature in excess of 1000" C. whereby gas may enter said tube between said jigs and said tube the area of clearance between each of said. jigs and said. tube being such that said entering gas cannot exceed its sonic velocity and be exhausted from said tube by said exhausting means.

7. The apparatus of claim 2, said heater tube being metal and said means to heat said heater tube being a source of alternating current connected therewith.

8. In an evacuation system, means forming an elongated passage of uniform cross-section open at both ends, means for carrying articles through said passage, a substantial length of said carrying means having a uniform cross-section and said uniform cross-section having a small clearance in said first mentioned means whereby gas may enter said passage between the inner surface of said passage and said transport means, the area of said small clearance being such that the entering gas cannot exceed its sonic velocity, gas exhausting means connected to said first mentioned means at spaced intervals therealong the length of said first mentioned means serviced by said exhausting means being sufficient to span a series of said carrying means, said exhausting means producing stations of progressively increasing vacuum proceeding from the vicinity of the References Cited in the file of this patent UNITED STATES PATENTS 1,528,133 Ross Mar. 3, 1925 1,967,346 Barnby July 24, 1934 1,969,717 Bach Aug. 14, 1934 2,162,768 Titchen et al. June 20, 1939 2,285,867 Minaker June 9, 1942 2,334,718 Lowry et al. Nov. 23, 1943 2,583,866 Mero Jan. 29, 1952 

